Cr-Mo alloy steel for transmission gear

ABSTRACT

Cr—Mo alloy steel suitable for motor vehicle transmission gears and shafts is provided and can avoid solve problems associated with. Preferred Cr—Mo alloy steel of the invention comprises steel as a major component, about 0.17 to about 0.21 weight % of carbon, about 0.15 weight % or less of silicon, about 0.60 to about 0.85 weight % of manganese, about 0.02 weight % or less of phosphorus, about 0.03 weight % or less of sulfur, about 1.25 to about 1.45 weight % of chrome, about 0.55 to about 0.65 weight % of molybdenum, and about 0.015 to about 0.035 weight % of niobium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Korean Application No. 10-2003-0067719, filed on Sep. 30, 2003, the disclosure of which is incorporated fully herein by reference.

FIELD OF THE INVENTION

The present invention relates to a high-strength chrome-molybdenum (Cr—Mo) alloy steel suitable for transmission gears and shafts. In particular, the present invention relates to the high-strength Cr—Mo alloy steel suitable for transmission gears and shafts, which has good physical properties with reduced cost and improved fabrication processing including reduced heat cycle times.

BACKGROUND OF THE INVENTION

The conventional procedure for manufacturing automobile transmission gears comprises steps of hot forging or cold forging of materials; cooling (air cooling or leaving at room temperature); heat treatment before the machining (ISO annealing or normalizing); machining (shaving and hobbing); carburizing heat treatment; and post processing (grinding, honing), as shown in FIG. 1.

Cr alloy, Cr—Mo alloy and Ni—Cr—Mo alloy steels have been widely used for manufacturing automobile transmission gears. Since the majority of alloy steel materials used for automobile transmission gears are used after carburizing heat treatment, it is preferable to select the alloy steel material which is suitable for each procedure, cheap and capable of maintaining good physical properties after the heat treatment.

Namely, the alloy steel material for automobile transmission gears preferably has good forgibility, machinability and physical properties (e.g., fatigue and impact properties), as well as favorable costs-of-production.

For example, Japanese patent publication Nos. Hei9-201644 and Hei4-88148 disclose a Cr alloy steel and Cr—Mo alloy steel, which are inexpensive, but since their fatigue and impact properties are poor, they have been mainly used for manufacturing gears that do not bear relatively high loads.

On the other hand, while Ni—Cr—Mo alloy steel has notable shortcomings such as significant expense due to the use of nickel and processing difficulties, its fatigue and impact properties are superior. Consequently, Ni—Cr—Mo alloy steel has been commonly used for manufacturing gears that may receive relatively high loads Japanese Patent No. Hei9-296250, and Japanese Patent No. Sho63-235452).

Since the price of nickel is relatively lower in North America and Europe than in Asia, motor companies in North America and Europe have employed the Ni—Cr—Mo alloy steel for manufacturing automobile gears and shafts.

In case of a carburizing steel for gears, molybdenum or nickel is added as an alloy element to increase hardenability, strength and toughness. However, nickel is expensive and causes several problems by unduly increasing the steel's toughness when added to the steel. For example, since nickel shows poor machinability, it can deteriorate the roughness of gear tooth surfaces, reduce lifetime of processing tools, and curtail productivity.

Accordingly, there has been in need of developing the Cr—Mo alloy steel which has superior hardenability and machinability, is economically feasible, and is capable of substituting for the Ni—Cr—Mo alloy steel.

SUMMARY OF THE INVENTION

Accordingly, in one aspect, the present invention provides a high-strength Cr—Mo alloy steel suitable for transmission gears and other vehicle components where the alloy is essentially or completely free of nickel. Such Cr—Mo alloy steel can avoid problems associated with use of nickel (e.g. such as that nickel added in the preparation of carburizing steel can be expensive and can deteriorate machinability of the steel and gears made of Ni—Cr—Mo alloy steel can pose processing difficulties such as reducing the productivity and operational lifetime of processing tools).

Preferred Cr—Mo alloy steel of the invention can exhibit superior physical properties with reduced manufacturing costs. In particular, preferred Cr—Mo alloy steel of the invention can avoid defects and shortcomings of existing Cr—Mo and Ni—Cr—Mo alloy steels without loss of desirable properties. Preferred Cr—Mo alloy steel of the invention can exhibit physical properties applicable to a high-strength, high-durability and compact design particularly suitable for use in manufacture of motor vehicle components such as automobile and truck transmission gears and shafts.

Additionally, the invention provides methods for producing Cr—Mo alloy steel which can include reduced heat treatment cycle times through high temperature carburizing due to the maximization of grain refining effect.

The invention also transmission gears and shafts and other vehicle parts and components that comprise the disclosed Cr—Mo alloy steel. In particular, preferred Cr—Mo alloy steel of the invention may be used to produce and in the construction of an Output Final Gear, Differential Drive Gear, Input and Output Shaft of a high power hand transmission, and the like.

It is understood that the term “vehicle” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles, buses, trucks, various commercial vehicles, watercraft, aircraft, and the like.

Other aspects of the invention are discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, wherein

FIG. 1 shows the procedure for manufacturing an automobile transmission gear, and

FIG. 2 shows the result of testing gear flexural fatigue.

DETAILED DESCRIPTION OF THE INVENTION

As discussed above, the invention provides Cr—Mo alloy that can exhibit properties that are particularly suitable for manufacture of vehicle parts and components.

Preferred Cr—Mo alloy steel of the invention suitably may comprise steel (Fe) as a major component, about 0.17 to about 0.21 weight % of carbon (C), about 0.15 weight % or less of silicon (Si), about 0.60 to about 0.85 weight % of manganese (Mn), about 0.02 weight % or less of phosphorus (P), about 0.03 weight % or less of sulfur (S), about 1.25 to about 1.45 weight % of chrome (Cr), about 0.55 to about 0.65 weight % of molybdenum (Mo), and about 0.015 to about 0.035 weight % of niobium (Nb). It is also preferred that dissolved oxygen is added to the above alloy-based component mixture at a concentration of about 15 ppm or less, which can enhance the soundness of the alloy. Preferably, one or more or all of silicon, phosphorus, sulfur and oxygen are present in the alloy.

Particularly preferred Cr—Mo alloy steel of the invention suitably may comprise 0.17 to 0.21 weight % of carbon (C), 0.1 weight % or less of silicon (Si), 0.65 to 0.85 weight % of manganese (Mn), 0.015 weight % or less of phosphorus (P), 0.025 weight % or less of sulfur (S), 1.3 to 1.45 weight % of chrome (Cr), 0.6 to 0.65 weight % of molybdenum (Mo), 0.02 to 0.035 weight % of niobium (Nb), oxygen as provided by addition of 15 ppm or less dissolved oxygen. Preferably, each of silicon, phosphorus, sultur and oxygen is present in the formed alloy steel composition, and the balance of the alloy steel composition is steel (Fe).

As mentioned above preferred Cr—Mo alloy steel of the invention is essentially or completely free of nickel. More particularly, preferred alloy steel of the invention has less than about 1 weight percent nickel, more preferably less than 0.5, 0.2 or 0.1 weight percent nickel, and particularly preferred Cr—Mo alloy steel of the invention is completely free of nickel.

Such reduction or absence of nickel during manufacture of the Cr—Mo alloy steel can significantly improve processability. It also has been found that physical properties of the alloy steel are not particularly compromised by the reduction or absence of nickel and can be at least substantially maintained through use of comparatively increased amounts of chrome and molybdenum relative to prior systems.

Unless indicated otherwise, references herein to weight percent or parts per million (ppm) or other similar percent or parts units are made based on 100 weight percent of the steel alloy composition or total parts of the steel alloy composition.

While not being limited by theory, preferred Cr—Mo alloy steel of the invention can minimize or avoid the problem of increased depth of surface intergranular oxidation layer through use of a relatively increased chrome content while limiting silicon (Si) content. Additionally, preferred Cr—Mo alloy steel of the invention can minimize or avoid the problem of molybdenum carbide precipitation (which can result with use of relatively high molybdenum content) by the relatively increased niobium (Nb) content which can provide higher carbide forming affinity than molybdenum.

Still further, in a preferred aspect, a relatively increased amount of sulfur may be employed to facilitate processing of the alloy steel that has enhanced strength due to increased chrome and molybdenum contents. More specifically, in certain preferred aspects, sulfur will be present in an amount of greater than about 0.01 or 0.02 weight percent, but no more than about 0.03 weight percent.

As discussed above, methods for producing Cr—Mo alloy steel also are provided. In one aspect, preferred production methods comprise admixing Fe (steel), about 0.17 to about 0.21 weight % of carbon, about 0.15 weight % or less of silicon, about 0.60 to about 0.85 weight % of manganese, about 0.02 weight % or less of phosphorus, about 0.03 weight % or less of sulfur, about 1.25 to about 1.45 weight % of chrome, about 0.55 to about 0.65 weight % of molybdenum, and about 0.015 to about 0.035 weight % of niobium. Oxygen may be dissolved in the admixture preferably in an amount of 15 ppm or less dissolved oxygen.

In more particular aspects, alloy steel of the invention may be produced by admixing of the components as disclosed above which can include one or more of hot or cold forging of those components; thereafter cooling of the forged material e.g. by air cooling or leaving at room temperature; heat treatment before the machining such as annealing or normalizing; machining such as shaving and/or hobbing; carburizing heat treatment; and post processing as may be desired such as grinding, honing, and the like.

Major components of preferred Cr—Mo alloy steel of the invention are set forth in the following Table 1 which shows the components of preferred Cr—Mo alloy steel according to the present invention as compared to those other Cr—Mo and Ni—Cr—Mo alloy steels. TABLE 1 Alloy steel Inventive alloy Existing alloy steels Content steel (Cr-Mo Cr-Mo based Ni-Cr-Mo based (weight %) based) ASCM17H1 SNCM518H 17CrNiMo6 C 0.17˜0.21 015˜0.21 0.15˜0.18 0.15˜0.20 Si ≦0.15  0.15˜0.35 ≦0.15  ≦0.40  Mn 0.60˜0.85 0.55˜0.90 0.50˜0.60 0.40˜0.60 P ≦0.020 ≦0.030 ≦0.025 ≦0.040 S ≦0.030 ≦0.030 0.01˜0.02 ≦0.040 Ni — — 1.55˜1.65 1.40˜1.70 Cr 1.25˜1.45 0.85˜1.25 0.50˜0.65 1.50˜1.80 Mo 0.55˜0.65 0.15˜0.35 0.55˜0.65 0.25˜0.35 Nb 0.015˜0.035 — 0.015˜0.025 — O₂ ≦15 ppm — — — Fe Residues Residue Residue Residue SNCM518H: a representative high strength steel for transmission gears of Japan Mitsubishi steel 17CrNiMo6: a representative high strength steel for transmission gears listed in DIN standard which has been widely used in Europe (in particular, Germany) motor companies ASCM17H1: a principal steel material for speed gears of Hyundai motor company

As discussed above, preferred Cr—Mo alloy steel of the present invention is essentially or completely free of nickel (Ni) to improve the processability and curtail costs. Preferred Cr—Mo alloy steel of the invention does comprise carbon suitably in the range of about 0.17 to about 0.21 weight % which can enhance desired physical properties including hardenability.

Additionally, for preferred Cr—Mo alloy steel of the invention, the content of silicon (Si) is suitably restricted to about 0.15 weight part or less based on 100 weight part of alloy steel which restricted amount can limit the thickness of the surface intergranular oxidation layer generated during the carburizing step of the steel alloy production. The relatively increased content of chrome employed in the steel alloy of the invention can provide a generally acceptable surface intergranular oxidation layer compared to existing Cr—Mo alloy steel. Thus, to avoid over-production of the surface intergranular oxidation layer, the content of silicon preferably does not exceed about 0.15 weight %. Preferably, a surface intergranular oxidation layer does not exceed about 15 μm in thickness.

As discussed above, preferred Cr—Mo alloy steel of the invention comprises chrome (Cr) in the range of about 1.25 to about 1.45 weight percent based on 100 weight percent of alloy steel. It has been found that use of chrome in amounts of less than about 1.25 weight percent may not provide physical properties that are improved relative to existing Cr—Mo alloy steel. Further, use of chrome in excess of 1.45 weight percent can pose one or more problems such as increased expense, increased brittleness (fragibility) due to the precipitation of chrome carbide (or Cr—Mo-based carbide) on the carburized layer of the surface during the carburizing step, and the surface intergranular oxidation layer can form at thicknesses of greater than about 15 μm even if the silicon content is restricted to about 0.15 weight % or less as discussed above.

As also discussed above, preferred Cr—Mo alloy steel of the invention comprises molybdenum (Mo) in the range of about 0.55 to about 0.65 weight percent based on 100 weight percent of alloy steel. This molybdenum content is higher than that of the existing Cr—Mo alloy steel. It has been found that use of molybdeneum in amounts of less than about 0.55 weight percent may not provide physical properties that are improved relative to existing Cr—Mo alloy steel. Further, use of molybdenum in excess of about 0.65 weight percent can pose one or more problems such as precipitation of Cr—Mo-based carbide at the boundary of the carburized layer and fine cracks forming around that boundary, which can result in increased brittleness.

To maintain high processability notwithstanding the improved physical property (high-strength) of the preferred steel alloy the invention, the maximum content of sulfur (S) is preferably increased to about 0.03 weight % which is higher than that of existing Cr—Mo alloy steel. This higher maximum sulfur content is well within a range that is viewed as harmless.

Further, to prevent grain coarsening during a high temperature carburizing step and maximize the grain refinement effect, preferred Cr—Mo alloy steel of the invention preferably contains niobium (Nb) in the range of about 0.015 to about 0.035 weight % based on 100 weight percent of alloy steel. Niobium is capable of preventing the grain growth by generating fine niobium nitride or carbide within the alloy steel. In case of using niobium in an amount of less than about 0.015 weight %, improvement of physical properties may be negligible, and in case of using niobium in an amount of more than about 0.035 weight %, undesired increased brittleness may occur due to the over-precipitation of carbide at the grain boundary.

In preferred Cr—Mo alloy steel of the invention, the maximum content of niobium is increased relative to existing Cr—Mo alloy steel. Such increased niobium content can prevent the generation of molybdenum carbide or chrome carbide which may otherwise occur due to the relatively increased amounts of chrome and/or molybdenum employed in steel alloy of the invention.

As also discussed above, preferred Cr—Mo alloy steel of the invention contains dissolved oxygen at a concentration of about 15 ppm or less based on the total parts of the alloy steel. Such restricted amounts of oxygen can minimize content of impurities in the alloy steel.

The following Examples and Test Examples are given for the purpose of illustration only, and they should not be construed as limiting the scope of the present invention.

EXAMPLES EXAMPLE AND COMPARATIVE EXAMPLES

Several types of alloy steels were manufactured according to the alloy components of Table 1 as described above.

The components of alloy steels manufactured as the preferred Example of the present invention and the Comparative Examples are described in Table 2. The alloy steels of Example and Comparative Examples were manufactured by a conventional method according to the components and contents of Table 2.

In Table 2, while Example was the alloy steel of the present invention, Comparative Examples 1 to 4 were the alloy steels manufactured to analyze the effect of alloy content on the physical property and Comparative Examples 5 to 7 were the alloy steels under producing and applying to transmission gears. TABLE 2 Alloy steel Com. Com. Com. Exp. 5 Exp. 6 Exp. 7 Content Com. Com. Com. Com. ASCM1 SNCM5 17CrNi (weight %) Exp. Exp. 1 Exp. 2 Exp. 3 Exp. 4 7H1 18H Mo6 C 0.18 0.18 0.17 0.18 0.18 0.20 0.18 0.16 Si 0.09 0.08 0.06 0.09 0.08 0.21 0.09 0.26 Mn 0.69 0.69 0.62 0.68 0.69 0.83 0.55 0.56 P 0.011 0.009 0.010 0.009 0.011 0.015 0.006 0.009 S 0.023 0.020 0.019 0.020 0.021 0.018 0.015 0.014 Ni — — — — — — 1.57 1.59 Cr 1.42 1.39 1.40 1.48 1.21 1.05 0.55 1.57 Mo 0.61 0.68 0.53 0.68 0.52 0.19 0.61 0.28 Nb 0.026 0.025 0.024 0.025 0.026 — 0.022 — O₂ 15 ppm 15 ppm 15 ppm 15 ppm 15 ppm — — — Fe Residues Residues Residues Residues Residues Residues Residues Residues

TEST EXAMPLE

The basic physical property of the alloy steels of Example and Comparative Examples of Table 2 necessary for transmission gears were analyzed and compared. The results were shown in Tables 3 and 4, and FIG. 2. Table 3 depicts the results of examining fatigue and impact properties after the carburizing heat treatment, and its measured value were shown as a representative value for convenience.

Table 4 shows the results of comparing the processability essential for the manufacture of transmission gears, which means a gear processing volume per 1 processing tool during the shaving processing step of a certain gear for manual transmission of a motor vehicle.

The processability of the inventive alloy steel of Example was examined and compared with those of the existing alloy steels of Comparative Examples of 5 and 6.

FIG. 2 illustrates the result of comparing the fatigue properties of the inventive alloy steel with the existing alloy steel of Comparative Example 7 presently applied as a high-strength material by European motor companies. TABLE 3 Rational bending fatigue test*¹⁾ Contact Gear bending fatigue test*⁴⁾ Surface Core Hardening Grain size Fatigue fatigue test*²⁾ Impact test*³⁾ Surface Hardening Fatigue hardness hardness depth (ASTM limit Limited cycle Impact value hardness depth limit Alloy steel (Hv) (Hv) (mm) No) (kef/mm²) (×10⁶) (kef/cm²) (Hv) (mm) (Nm) Exp. 763 430 0.80 10.3 96 7.8 1.71 770 0.7  800 Com. Exp. 1 807 472 0.87 10.4 92 6.1 0.85 — — — Com. Exp. 2 751 400 0.74 10.2 87 7.0 2.10 — — — Com. Exp. 3 810 481 0.92 10.4 92 6.0 0.61 — — — Com. Exp. 4 752 394 0.72 10.0 85 3.8 0.92 — — — Com. ASCM17H1 742 391 0.7   8.4 78 1.4 0.75 — — — Exp. 5 Com. SNCM518H 744 415 0.8  10.0 95 7.3 1.65 — — — Exp. 6 Com. 17CrNiMo6 — — — — — — — 714 0.65 680 Exp. 7 □heat treatment cycle of all samples: carburizing (900° C., 2 hrs) → oil hardening (oil temperature: 150° C.) → tempering (170° C., 2 hrs) □conditions of each test are same and methods thereof are described as follows. The hardening depth is the depth from the surface to the core (based on Hv 550) *¹⁾the test is carried out according to JIS Z 2272 and 1-8 test samples are used as a test sample. *²⁾the test is carried out according to Charpy impact test method and JIS Z 2202 No3 test sample is used as a test sample. *³⁾which means the number of impact until pitting (or fitting) occurs at 332 kef/mm² of surface pressure, 40% of slip ratio and 50% of oil temperature *⁴⁾which is a reference as a result of comparing with Spur type gear having 1.95 of Normal module, 29 of tooth number, 18.738° of pressure angle, 62.969 mm of tooth outer diameter, 57.404 mm of PCD (Pitch Circle Diameter), and 31 mm of tooth width *⁵⁾see FIG. 2 (for the comparison with Europe major steels, two kinds of steels are tested)

TABLE 4 Exp. (inventive Com. Exp. 5 Com. Exp. 6 steel) ASCM17H1 SNCM518H Shaving cutter About 1600 About 2000 About 1200 processability*¹⁾(large) *¹⁾Shaving cutter processability means the total processed number of a tool for its life during the shaving process for hand transmission gears (which is carried out before the carburizing heat treatment)

As shown in Table 3, although the tested alloy steel of the present invention did not contain any nickel (Ni), it showed significantly higher physical property than the Cr—Mo based alloy steel of Comparative Example 5 and equal or higher physical property than the Ni—Cr—Mo based alloy steels of Comparative Examples 6 and 7.

As a result of adjusting the contents of chrome and molybdenum, when the contents of two alloy components exceeded the preferred contents of the present invention (Comparative Examples 1 and 3), there were several problems namely that their brittleness was increased by excessively precipitating Cr—Mo-based carbide at the boundary of carburized surface hardening layer as well as the hardenability was increased (reduction of impact value).

Meanwhile, in case of lowering the contents of chrome and molybdenum to below preferred amounts of the present invention, it was found that the resulting alloy fatigue-related property was significantly deteriorated.

Further, in case of adding niobium (Nb), the effect of grain refinement was superior to that in case of having no niobium (Comparative Example 5), and since the addition of niobium made it possible to conduct the carburizing treatment at high temperature, it could be expected to reduce the time for heat treatment cycle.

As a result of examining the processability, as shown in Table 4 above, it was found that the inventive alloy steel of the test Example showed a remarkably higher processability than the Ni—Cr—Mo based alloy steel of Comparative Example 6 (about 33%), which indicates that the potential processability problem arising from improved strength can be resolved by relatively increased sulfur (S) content in accordance with the invention.

As described above, the preferred Cr—Mo alloy steel of the present invention can provide reduced cost-of-production relative to Ni—Cr—Mo alloy steel that contains relatively expensive amounts of nickel. Additionally, preferred Cr—Mo alloy steel of the invention can exhibit similar or improved physical properties relative to existing alloy steels such as Ni—Cr—Mo alloy steels. Further, since the preferred Cr—Mo alloy steel of the invention is capable for use in high power transmission gears and shafts, the alloy steel can reduce costs and prolong operating lifetimes of processing tools. In particular, the preferred inventive Cr—Mo alloy steel can exhibit properties advantageous to gears and shafts (including e.g. Output Final Gear, Differential Drive Gear, Input and Output Shaft of a high power hand transmission, and the like) that during use can bear loads that are considered excessive for existing Cr—Mo alloy steel.

All documents mentioned herein are incorporated by reference herein in their entirety.

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the disclosure, may make modifications and improvements within the scope and spirit of the invention. 

1. A Cr—Mo alloy steel, comprising steel as a major component, about 0.17 to about 0.21 weight % of carbon, about 0.15 weight % or less of silicon, about 0.60 to about 0.85 weight % of manganese, about 0.02 weight % or less of phosphorus, about 0.03 weight % or less of sulfur, about 1.25 to about 1.45 weight % of chrome, about 0.55 to about 0.65 weight % of molybdenum, and about 0.015 to about 0.035 weight % of niobium.
 2. The alloy steel of claim 1 wherein the alloy steel is formed by addition of 15 ppm or less dissolved oxygen to the alloy steel mixture.
 3. The alloy steel of claim 1 wherein the alloy steel comprises one or more of silicon, phosphorus, sulfur and oxygen.
 4. The alloy steel of claim 1 wherein the alloy steel comprises silicon, phosphorus, sulfur and oxygen.
 5. The alloy steel of claim 1 wherein the Cr—Mo alloy steel comprises 0.17 to 0.21 weight % of carbon, 0.1 weight % or less of silicon, 0.65 to 0.85 weight % of manganese, 0.015 weight % or less of phosphorus, 0.025 weight % or less of sulfur, 1.3 to 1.45 weight % of chrome, 0.6 to 0.65 weight % of molybdenum, 0.02 to 0.035 weight % of niobium, and oxygen as provided by addition of 15 ppm or less dissolved oxygen.
 6. The alloy steel of claim 1 wherein the Cr—Mo alloy is at least essentially free of nickel.
 7. The alloy steel of claim 1 wherein the Cr—Mo alloy is completely free of nickel.
 8. An alloy steel comprising: about 0.17 to about 0.21 weight % of carbon, about 0.15 weight % or less of silicon, about 0.60 to about 0.85 weight % of manganese, about 0.02 weight or less of phosphorus, about 0.03 weight or less of sulfur, about 1.25 to about 1.45 weight % of chrome, about 0.55 to about 0.65 weight % of molybdenum, about 0.015 to about 0.035 weight % of niobium, and oxygen as provided by addition of 15 ppm or less dissolved oxygen, with balance being steel.
 9. The alloy steel of claim 8 wherein the alloy steel is at least essentially free of nickel.
 10. A method for producing an alloy steel comprising: admixing steel, about 0.17 to about 0.21 weight % of carbon, about 0.15 weight % or less of silicon, about 0.60 to about 0.85 weight % of manganese, about 0.02 weight % or less of phosphorus, about 0.03 weight % or less of sulfur, about 1.25 to about 1.45 weight % of chrome, about 0.55 to about 0.65 weight % of molybdenum, and about 0.015 to about 0.035 weight % of niobium.
 11. The method of claim 10 wherein the alloy steel is at least essentially free of nickel.
 12. A vehicle component comprising alloy steel of claim
 1. 13. The component of claim 12 wherein the component comprising the alloy steel is a transmission gear of a motor vehicle.
 14. The component of claim 12 wherein the component comprising the alloy steel is a transmission shaft of a motor vehicle. 